The present invention relates generally to transom mounts for coupling an outboard motor to a fishing boat. More specifically, our invention relates to a versatile transom jack designed for small fishing boats which is capable of simultaneously varying motor height and trim.
Transom mounts for mounting outboard motors to watercraft are well established in the art. Use of conventional transom mounts permits the user to selectively position the motor cavitation plate for improved efficiency of operation. In addition, transom mounts greatly facilitate trailering the boat. Transom mounts are advantageous to adapt a boat for varying loads and speeds. For example, the operator may position the cavitation plate lower in the water to obtain maximum thrust at low speeds when the boat is used for towing or other work, and subsequently raise the plate for operation at higher speeds. Correct location of the cavitation plate relative to the bottom of the boat is critical, particularly with small fishing boats.
Fishing boats typically include a rear transom for mounting the motor, angled at approximately eighteen degrees relative to the perpendicular. When a motor is mounted to the transom, it too will be oriented at substantially eighteen degrees, and its operative parts must be designed properly to dispose them in proper orientation. Improper orientation of the propeller, given the speed selected, for example, can lead to cavitation. However, the best disposition for the propeller and the best angle of orientation of the cavitation plate are functions of speed, boat weighting or load, and the depth of the water. Where a small, heavily loaded boat is traversing shallow water, for example, the motor must be raised to prevent the propeller from slamming into the bottom.
However, when a fishing motor is raised to "clear" for shallow depths, the orientation of the prop and the cavitation plate should be readjusted to angle the boat for proper planing and optimum thrust. In other words, the orientation of the prop's axis of rotation and the cavitation plate must be adjusted as a function of motor height.
It is also desirable to control the trim or angular orientation of the plate relative to the bottom of the boat. When the plate is angled into the water, for example, the propeller "digs" into the water and produces a greater thrust moment. At higher speeds, less angle is desired so that the cavitation plate provides minimum resistance. As will be appreciated by those experienced in the operation of small watercraft, vertical and angular motor relationships are closely interrelated. Maximum operating efficiency and comfort can only be achieved by proper adjustment of both, to achieve the desired combination of thrust and speed.
A variety of transom mounts directed to controlling the trim and/or height of outboard motors have been proposed in the prior art. For example, U.S. Pat. No. 4,778,417 issued to Mixon, Jr. on Oct. 18, 1988 discloses a transom bracket coupled to the boat by a pair of hydraulic cylinders which raise and lower the bracket. An additional cylinder is coupled to the motor head to adjust the motor tilt. Blanchard U.S. Pat. No. 4,504,237 issued Mar. 12, 1985 defines an outboard motor mount having hydraulically controlled swivel brackets for positioning the motor. In the latter device, tilt is controlled by cooperation of a pivot arm movable within follower slots associated with opposite sides of the mount. A fine trim adjustment mechanism is proposed for use in conjunction with a manually tiltable motor mount by MacGregor, in U.S. Pat. No. 4,682,959, issued July 28, 1987. A plurality of hydraulic cylinders provide tilt and trim adjustment in a transom mount adaptor proposed by Peirce in U.S. Pat. No. 4,687,448, issued Aug. 18, 1987. Prior art transom mount patents which are believed of greatest relevance to the present invention are the following: U.S. Pat. No. 4,778,415, issued Oct. 18, 1988 to Knotts; Cook, U.S. Pat. No. 4,482,330, issued Nov. 13, 1984; and, U.S. Pat. No. 4,624,438 issued to Goodman, Jr. on Nov. 25, 1986.
Knotts proposes a transom bracket which permits the operator to selectively control motor trim by activating hydraulic cylinders which displace the motor mount vertically relative to the transom mount. Motor height is controlled by separately operable pivot brackets. Cook provides a mount comprising a motor bracket slidably coupled to a transom bracket. Vertical displacement of the motor is limited by opposing pairs of follower slots defined parallel to the longitudinal axis of the transom bracket. A single hydraulic cylinder disposed within the interior of the mount controls movement of the motor via a remote control positioned within the boat. The outboard transom mounting defined in the latter Goodman '438 reference comprises a pair of motor brackets slidably coupled to a pair of transom brackets. Cooperating pairs of elongated follower slots defined longitudinally through the sides of the transom brackets limit vertical travel of the motor brackets relative to the boat. Movement of the motor brackets is controlled by winding and unwinding a ratchet-controlled cable associated with the motor bracket.
However, the known prior art does not disclose a transom mount which provides convenient means for simultaneously controlling both trim and vertical displacement of the motor. Thus it would seem desirable to provide a transom mount for small watercraft which conveniently adjusts both in a coordinated movement to maintain maximum operating efficiency and comfort in a wide variety of orientations.